The present invention relates to integrated circuits which perform clock/calendar maintenance functions (alone or in combination with other functions).
The present invention, in the presently preferred embodiment, provides a clock/calendar circuit, within an integrated circuit, wherein a dedicated hardware register tracks the hundredths-of-second data, but uses software registers for the other clock/calendar information (including seconds, minutes, hours, day, date, month, and year information).
A more common way to implement this functionality would be to track essentially all of this data in hardware, or track essentially all of it in software. An example of the former approach is the DS1215 integrated circuit (or DS1216 socket), and an example of the latter approach is the integrated circuit in the DS1287 timing module; both of these parts, and their data sheets, are available from Dallas Semiconductor Corporation (DSC), 4350 Beltwood Parkway South, Dallas 75244. The contents of both of these parts, and their descriptions in the 1988 DSC Data Book, are hereby incorporated by reference.
The use of programmable logic for the more significant fields of data saves space, and provides system designers with additional flexibility. However, in a low power circuit, it has been discovered that tracking the hundredths data in software leads to excess power consumption: although the standby power of the circuits may be small, the charge transferred during the 100 active operations every second produces a significant net average power consumption.
Thus, the division of the hardware and software implementation of timekeeping functions helps to provide optimal compactness and power consumption. Thus, this combination is advantageous, and is particularly advantageous in a battery-backed circuit, where power must be stringently conserved.